Fabrication of correlated electron material devices method to control carbon

ABSTRACT

Subject matter disclosed herein may relate to fabrication of correlated electron materials used, for example, to perform a switching function. In embodiments, precursors, in a gaseous form, may be utilized in a chamber to build a film of correlated electron materials comprising various impedance characteristics.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No.15/048,778, titled “METHOD PROVIDING FOR A STORAGE ELEMENT,” filed onFeb. 19, 2016, and incorporated herein by reference in its entirety.This application is also a divisional of U.S. patent application Ser.No. 15/048,244, titled “FABRICATION OF CORRELATED ELECTRON MATERIALDEVICES METHOD TO CONTROL CARBON,” and filed on Feb. 16, 2016, which isassigned to the assignee of claimed subject matter and incorporatedherein by reference in its entirety.

BACKGROUND Field

Subject matter disclosed herein relates to correlated electron devices,and may relate, more particularly, to approaches toward fabricatingcorrelated electron devices, such as may be used in switches, memorycircuits, and so forth, exhibiting desirable impedance characteristics.

Integrated circuit devices, such as electronic switching devices, forexample, may be found in a wide range of electronic device types. Forexample, memory and/or logic devices may incorporate electronic switchesthat may be used in computers, digital cameras, cellular telephones,tablet devices, personal digital assistants, and so forth. Factorsrelated to electronic switching devices, such as may be incorporated inmemory and/or logic devices, which may be of interest to a designer inconsidering suitability for any particular application may includephysical size, storage density, operating voltages, impedance ranges,and/or power consumption, for example. Other example factors that may beof interest to designers may include cost of manufacture, ease ofmanufacture, scalability, and/or reliability. Moreover, there appears tobe an ever-increasing need for memory and/or logic devices that exhibitcharacteristics of lower power and/or higher speed.

BRIEF DESCRIPTION OF THE DRAWINGS

Claimed subject matter is particularly pointed out and distinctlyclaimed in the concluding portion of the specification. However, both asto organization and/or method of operation, together with objects,features, and/or advantages thereof, it may best be understood byreference to the following detailed description if read with theaccompanying drawings, in which:

FIG. 1A is a diagram showing an example current density versus voltageprofile of a device formed from a correlated electron material accordingto an embodiment;

FIG. 1B is a schematic diagram of an equivalent circuit of a correlatedelectron material switch according to an embodiment;

FIG. 1C is a diagram showing a layered structure where the CEM films arebounded by electrodes and the CEM films vary in dopant, for example thecenter film may be less doped than the outer CEM films.

FIG. 2A-2C show simplified flowcharts of methods for fabricatingcorrelated electron material films that comprise carbon or other dopantspecies concentrations controlled according to one or more embodiments;

FIG. 3 is a diagram of a nickel dicyclopentadienyl molecule (Ni(C₅H₅)₂,which may be abbreviated as Ni(Cp)₂, and which may function as aprecursor to be utilized in fabrication of correlated electron materialsaccording to an embodiment;

FIGS. 4A-4L show sub-processes utilized in a method for fabricatingcorrelated electron material devices according to an embodiment;

FIGS. 5A-5D are diagrams showing gas flow and temperature profiles, as afunction of time, which may be used in a method for fabricatingcorrelated electron material devices according to an embodiment;

FIGS. 5E-5H are diagrams showing precursor flow and temperatureprofiles, as a function of time, which may be used in a method forfabricating correlated electron device materials according to anembodiment; and

FIGS. 6A-6C are diagrams showing temperature profiles, as a function oftime, used in deposition and annealing processes for fabricatingcorrelated electron material devices according to an embodiment.

Reference is made in the following detailed description to accompanyingdrawings, which form a part hereof, wherein like numerals may designatelike parts throughout to indicate corresponding and/or analogouscomponents. It will be appreciated that components illustrated in thefigures have not necessarily been drawn to scale, such as for simplicityand/or clarity of illustration. For example, dimensions of somecomponents may be exaggerated relative to other components.Additionally, it is to be understood that other embodiments may beutilized. Further, structural and/or other changes may be made withoutdeparting from claimed subject matter. It should also be noted thatdirections and/or references, for example, such as up, down, top,bottom, and so on, may be used to facilitate discussion of drawingsand/or are not intended to restrict application of claimed subjectmatter. Therefore, the following detailed description is not to be takento limit claimed subject matter and/or equivalents.

DETAILED DESCRIPTION

References throughout this specification to “one implementation,” “animplementation,” “one embodiment,” “an embodiment,” and/or the like,means that a particular feature, structure, and/or characteristicdescribed in connection with a particular implementation and/orembodiment is included in at least one implementation and/or embodimentof claimed subject matter. Thus, appearances of such phrases, forexample, in various places throughout this specification are notnecessarily intended to refer to the same implementation or to any oneparticular implementation described. Furthermore, it is to be understoodthat particular features, structures, and/or characteristics describedare capable of being combined in various ways in one or moreimplementations and, therefore, are within intended claim scope, forexample. In general, of course, these and other issues vary withcontext. Therefore, particular context of description and/or usageprovides helpful guidance regarding inferences to be drawn.

As utilized herein, the terms “coupled,” “connected,” and/or similarterms are used generically. It should be understood that these terms arenot intended as synonyms. Rather, “connected” is used generically toindicate that two or more components, for example, are in directphysical, including electrical, contact; while “coupled” is usedgenerically to mean that two or more components are potentially indirect physical, including electrical, contact; however, “coupled” isalso used generically to also mean that two or more components are notnecessarily in direct contact, but nonetheless are able to cooperateand/or interact. The term coupled is also understood generically to meanindirectly connected, for example, in an appropriate context.

The terms, “and,” “or,” “and/or” and/or similar terms, as used herein,include a variety of meanings that also are expected to depend, at leastin part, upon the particular context in which such terms are used.Typically, “or” if used to associate a list, such as A, B, or C, isintended to mean A, B, and C, here used in the inclusive sense, as wellas A, B, or C, here used in the exclusive sense. In addition, the term“one or more” and/or similar terms is used to describe any feature,structure, and/or characteristic in the singular and/or is also used todescribe a plurality and/or some other combination of features,structures and/or characteristics. Likewise, the term “based on” and/orsimilar terms are understood as not necessarily intending to convey anexclusive set of factors, but to allow for existence of additionalfactors not necessarily expressly described. Of course, for all of theforegoing, particular context of description and/or usage provideshelpful guidance regarding inferences to be drawn. It should be notedthat the following description merely provides one or more illustrativeexamples and claimed subject matter is not limited to these one or moreillustrative examples; however, again, particular context of descriptionand/or usage provides helpful guidance regarding inferences to be drawn.

Particular aspects of the present disclosure describe methods and/orprocesses for preparing and/or fabricating correlated electron materials(CEMs) to form a correlated electron switch, for example, such as may beutilized to form a correlated electron random access memory (CERAM) inmemory and/or logic devices, for example. Correlated electron materials,which may be utilized in the construction of CERAM devices and CEMswitches, for example, may also comprise a wide range of otherelectronic circuit types, such as, for example, memory controllers,memory arrays, filter circuits, data converters, optical instruments,phase locked loop circuits, microwave and millimeter wave transceivers,and so forth, although claimed subject matter is not limited in scope inthese respects. In this context, a CEM switch may exhibit asubstantially rapid conductor-to-insulator transition, which may bebrought about by electron correlations rather than solid statestructural phase changes, such as in response to a change from acrystalline to an amorphous state, for example, in a phase change memorydevice or, in another example, formation of filaments in resistive RAMdevices. In one aspect, a substantially rapid conductor-to-insulatortransition in a CEM device may be responsive to a quantum mechanicalphenomenon, in contrast to melting/solidification or filament formation,for example, in phase change and resistive RAM devices. Such quantummechanical transitions between relatively conductive and relativelyinsulative states, and/or between first and second impedance states, forexample, in a CEM may be understood in any one of several aspects. Asused herein, the terms “relatively conductive state,” “relatively lowerimpedance state,” and/or “metal state” may be interchangeable, and/ormay, at times, be referred to as a “relatively conductive/lowerimpedance state.” Similarly, the terms “relatively insulative state” and“relatively higher impedance state” may be used interchangeably herein,and/or may, at times, be referred to as a relatively “insulative/higherimpedance state.”

In an aspect, a quantum mechanical transition of a correlated electronmaterial between a relatively insulative/higher impedance state and arelatively conductive/lower impedance state, wherein the relativelyconductive/lower impedance state is substantially dissimilar from theinsulated/higher impedance state, may be understood in terms of a Motttransition. In accordance with a Mott transition, a material may switchfrom a relatively insulative/higher impedance state to a relativelyconductive/lower impedance state if a Mott transition condition occurs.The Mott criteria may be defined by (n_(c))^(1/3)a≈0.26, wherein n_(c)denotes a concentration of electrons, and wherein “a” denotes the Bohrradius. If a threshold carrier concentration is achieved, such that theMott criteria is met, the Mott transition is believed to occur.Responsive to the Mott transition occurring, the state of the CEM devicechanges from a relatively higher resistance/higher capacitance state(e.g., an insulative/higher impedance state) to a relatively lowerresistance/lower capacitance state (e.g., a conductive/lower impedancestate) that is substantially dissimilar from the higherresistance/higher capacitance state.

In another aspect, the Mott transition may be controlled by alocalization of electrons. If carriers, such as electrons, for example,are localized, a strong coulomb interaction between the carriers isbelieved to split the bands of the CEM to bring about a relativelyinsulative (relatively higher impedance) state. If electrons are nolonger localized, a weak coulomb interaction may dominate, which maygive rise to a removal of band splitting, which may, in turn, bringabout a metal (conductive) band (relatively lower impedance state) thatis substantially dissimilar from the relatively higher impedance state.

Further, in an embodiment, switching from a relatively insulative/higherimpedance state to a substantially dissimilar and relativelyconductive/lower impedance state may bring about a change in capacitancein addition to a change in resistance. For example, a CEM device mayexhibit a variable resistance together with a property of variablecapacitance. In other words, impedance characteristics of a CEM devicemay include both resistive and capacitive components. For example, in ametal state, a CEM device may comprise a relatively low electric fieldthat may approach zero, and therefore may exhibit a substantially lowcapacitance, which may likewise approach zero.

Similarly, in a relatively insulative/higher impedance state, which maybe brought about by a higher density of bound or correlated electrons,an external electric field may be capable of penetrating the CEM and,therefore, the CEM may exhibit higher capacitance based, at least inpart, on additional charges stored within the CEM. Thus, for example, atransition from a relatively insulative/higher impedance state to asubstantially dissimilar and relatively conductive/lower impedance statein a CEM device may result in changes in both resistance andcapacitance, at least in particular embodiments. Such a transition maybring about additional measurable phenomena, and claimed subject matteris not limited in this respect.

In an embodiment, a device formed from a CEM may exhibit switching ofimpedance states responsive to a Mott-transition in a majority of thevolume of the CEM comprising a device. In an embodiment, a CEM may forma “bulk switch.” As used herein, the term “bulk switch” refers to atleast a majority volume of a CEM switching a device's impedance state,such as in response to a Mott-transition. For example, in an embodiment,substantially all CEM of a device may switch from a relativelyinsulative/higher impedance state to a relatively conductive/lowerimpedance state or from a relatively conductive/lower impedance state toa relatively insulative/higher impedance state responsive to aMott-transition. In an embodiment, a CEM may comprise one or moretransition metals, or more transition metal compounds, one or moretransition metal oxides (TMOs), one or more oxides comprising rare earthelements, one or more oxides of one or more f-block elements of theperiodic table, one or more rare earth transitional metal oxideperovskites, yttrium, and/or ytterbium, although claimed subject matteris not limited in scope in this respect. In an embodiment, a CEM devicemay comprise one or more materials selected from a group comprisingaluminum, cadmium, chromium, cobalt, copper, gold, iron, manganese,mercury, molybdenum, nickel, palladium, rhenium, ruthenium, silver, tin,titanium, vanadium, and zinc (which may be linked to an anion, such asoxygen or other types of ligands), or combinations thereof, althoughclaimed subject matter is not limited in scope in this respect.

FIG. 1A is a diagram showing an example current density versus voltageprofile of a device formed from a CEM according to an embodiment 100.Based, at least in part, on a voltage applied to terminals of a CEMdevice, for example, during a “write operation,” the CEM device may beplaced into a relatively low-impedance state or a relativelyhigh-impedance state. For example, application of a voltage V_(set) anda current density J_(set) may place the CEM device into a relativelylow-impedance memory state. Conversely, application of a voltageV_(reset) and a current density J_(reset) may place the CEM device intoa relatively high-impedance memory state. As shown in FIG. 1A, referencedesignator 110 illustrates the voltage range that may separate V_(set)from V_(reset). Following placement of the CEM device into anhigh-impedance state or low-impedance state, the particular state of theCEM device may be detected by application of a voltage V_(read) (e.g.,during a read operation) and detection of a current or current densityat terminals of the CEM device.

According to an embodiment, the CEM device of FIG. 1A may include anytransition metal oxide (TMO), such as, for example, perovskites, Mottinsulators, charge exchange insulators, and Anderson disorderinsulators. In particular implementations, a CEM device may be formedfrom switching materials, such as nickel oxide, cobalt oxide, ironoxide, yttrium oxide, and perovskites, such as chromium doped strontiumtitanate, lanthanum titanate, and the manganate family includingpraseodymium calcium manganate, and praseodymium lanthanum manganite,just to provide a few examples. In particular, oxides incorporatingelements with incomplete “d” and “f” orbital shells may exhibitsufficient impedance switching properties for use in a CEM device. Otherimplementations may employ other transition metal compounds withoutdeviating from claimed subject matter.

In one aspect, the CEM device of FIG. 1A may comprise materials of thegeneral form AB:L_(x) (such as NiO:CO) that are transition metal,transition metal compounds, or transition metal oxide variable impedancematerials; though it should be understood that these are exemplary onlyand are not intended to limit claimed subject matter. Particularimplementations may employ other variable impedance materials as well.Nickel oxide, NiO, is disclosed as one particular TMO. NiO materialsdiscussed herein may be doped with extrinsic ligands, L_(x) which mayestablish and/or stabilize variable impedance properties. In particular,NiO variable impedance materials disclosed herein may include acarbon-containing ligand such as carbonyl (CO), forming NiO:CO. Inanother particular example, NiO doped with extrinsic ligands may beexpressed as NiO:L_(x), where L_(x) is a ligand element or compound andx indicates a number of units of the ligand for one unit of NiO. Oneskilled in the art may determine a value of x for any specific ligandand any specific combination of ligand with NiO or any other transitionmetal compound simply by balancing valences. In particular, NiO variableimpedance materials disclosed herein may include carbon containingmolecules of the form CaHbNdOf (in which a≥1, and b, d and f≥0) such as:carbonyl (CO), cyano (CN⁻), ethylene diamine (C₂H₈N₂),phen(1,10-phenanthroline) (C₁₂H₈N₂), bipyridine (C₁₀,H₈N₂),ethylenediamine ((C₂H₄(NH₂)₂), pyridine (C₅H₅N), acetonitrile (CH₃CN),and cyanosulfanides such as thiocyanate (NCS⁻), for example.

In accordance with FIG. 1A, if sufficient bias is applied (e.g.,exceeding a band-splitting potential) and the aforementioned Mottcondition is satisfied (e.g., injected electron holes are of apopulation comparable to a population of electrons in a switchingregion, for example), a CEM device may switch from a relativelylow-impedance state to a substantially dissimilar impedance state, suchas a relatively high-impedance state, responsive to a Mott transition.This may correspond to point 108 of the voltage versus current densityprofile of FIG. 1A. At, or suitably nearby this point, electrons are nolonger screened and become localized near the metal ion. Thiscorrelation may result in a strong electron-electron interactionpotential which may operate to split the bands to form a relativelyhigh-impedance material. If the CEM device comprises a relativelyhigh-impedance state, current may be generated by transportation ofelectron holes. Consequently, if a threshold voltage is applied acrossterminals of the CEM device, electrons may be injected into ametal-insulator-metal (MIM) diode over the potential barrier of the MIMdevice. If a threshold current of electrons is injected and a thresholdpotential is applied across terminals to place the CEM device into a“set” state, an increase in electrons may screen incoming electrons andremove a localization of electrons, which may operate to collapse theband-splitting potential, thereby bringing about a relativelylow-impedance state.

According to an embodiment, current in a CEM device may be controlled byan externally applied “compliance” condition, which may be determined atleast partially on the basis of an applied external current, which maybe limited during a write operation, for example, to place the CEMdevice into a relatively high-impedance state. This externally-appliedcompliance current may, in some embodiments, also set a condition of acurrent density for a subsequent reset operation to place the CEM deviceinto a relatively high-impedance state. As shown in the particularimplementation of FIG. 1A, a current density J_(comp) may be appliedduring a write operation at point 116 to place the CEM device into arelatively high-impedance state, may determine a compliance conditionfor placing the CEM device into a low-impedance state in a subsequentwrite operation. As shown in FIG. 1A, the CEM device may be subsequentlyplaced into a low-impedance state by application of a current densityJ_(reset)≥J_(comp) at a voltage V_(reset) at point 108, at whichJ_(comp) is externally applied.

In embodiments, compliance may set a number of electrons in a CEM devicewhich may be “captured” by holes for the Mott transition. In otherwords, a current applied in a write operation to place a CEM device intoa relatively low-impedance memory state may determine a number of holesto be injected to the CEM device for subsequently transitioning the CEMdevice to a relatively high-impedance memory state.

As pointed out above, a reset condition may occur in response to a Motttransition at point 108. As pointed out above, such a Mott transitionmay bring about a condition in a CEM device in which a concentration ofelectrons n approximately equals, or becomes at least comparable to, aconcentration of electron holes p. This condition may be modeledaccording to expression (1) as follows:

$\begin{matrix}{{\lambda_{TF}n^{\frac{1}{3}}} = {\left. C \right.\sim 0.26}} & (1) \\{n = \left( \frac{C}{\lambda_{TF}} \right)^{3}} & \;\end{matrix}$In expression 1, λ_(TF) corresponds to a Thomas Fermi screening length,and C is a constant.

According to an embodiment, a current or current density in region 104of the voltage versus current density profile shown in FIG. 1A, mayexist in response to injection of holes from a voltage signal appliedacross terminals of a CEM device. Here, injection of holes may meet aMott transition criterion for the low-impedance state to high-impedancestate transition at current I_(MI) as a threshold voltage V_(MI) isapplied across terminals of a CEM device.

This may be modeled according to expression (2) as follows:

$\begin{matrix}{{{I_{MI}\left( V_{MI} \right)} = {\frac{{dQ}\left( V_{MI} \right)}{dt} \approx \frac{Q\left( V_{MI} \right)}{t}}}{{Q\left( V_{MI} \right)} = {{qn}\left( V_{MI} \right)}}} & (2)\end{matrix}$Where Q(V_(MI)) corresponds to the charged injected (holes or electrons)and is a function of an applied voltage. Injection of electrons and/orholes to enable a Mott transition may occur between bands and inresponse to threshold voltage V_(MI), and threshold current I_(MI). Byequating electron concentration n with a charge concentration to bringabout a Mott transition by holes injected by I_(MI) in expression (2)according to expression (1), a dependency of such a threshold voltageV_(MI) on Thomas Fermi screening length λ_(TF) may be modeled accordingto expression (3), as follows:

$\begin{matrix}{{I_{MI}\left( V_{MI} \right)} = {\frac{Q\left( V_{MI} \right)}{t} = {\frac{{qn}\left( V_{MI} \right)}{t} = {\frac{q}{t}\left( \frac{C}{\lambda_{TF}} \right)^{3}}}}} & (3) \\{{J_{reset}\left( V_{MI} \right)} = {{J_{MI}\left( V_{MI} \right)} = {\frac{I_{MI}\left( V_{MI} \right)}{A_{CEM}} = {\frac{q}{A_{CEM}t}\left( \frac{C}{\lambda_{TF}\left( V_{MI} \right)} \right)^{3}}}}} & \;\end{matrix}$In which A_(CEM) is a cross-sectional area of a CEM device; andJ_(reset)(V_(MI)) may represent a current density through the CEM deviceto be applied to the CEM device at a threshold voltage which may placethe CEM device in a relatively high-impedance state.

FIG. 1B depicts a schematic diagram of an equivalent circuit of anexample CEM switch device according to an embodiment 150. As previouslymentioned, a correlated electron device, such as a CEM switch, a CERAMarray, or other type of device utilizing one or more correlated electronmaterials may comprise variable or complex impedance device that mayexhibit characteristics of both variable resistance and variablecapacitance. In other words, impedance characteristics for a CEMvariable impedance device, such as the device according to embodiment150, may depend at least in part on resistance and capacitancecharacteristics of the device if measured across device terminals 122and 130, for example. In an embodiment, an equivalent circuit for avariable impedance device may comprise a variable resistor, such asvariable resistor 126, in parallel with a variable capacitor, such asvariable capacitor 128. Of course, although a variable resistor 126 andvariable capacitor 128 are depicted in FIG. 1A as comprising discretecomponents, a variable impedance device, such as device of embodiment150, may comprise a substantially homogenous CEM and claimed subjectmatter is not limited in this respect.

Table 1 below depicts an example truth table for an example variableimpedance device, such as the device of embodiment 150.

TABLE 1 Correlated Electron Switch Truth Table Resistance CapacitanceImpedance R_(high)(V_(applied)) C_(high)(V_(applied))Z_(high)(V_(applied)) R_(low)(V_(applied)) C_(low)(V_(applied))~0Z_(low)(V_(applied))

In an embodiment, Table 1 shows that a resistance of a variableimpedance device, such as the device of embodiment 150, may transitionbetween a low-impedance state and a substantially dissimilarhigh-impedance state as a function at least partially dependent on avoltage applied across the CEM device. In an embodiment, an impedanceexhibited at a low-impedance state may be approximately in the range of10.0-100,000.0 times lower than a substantially dissimilar impedanceexhibited in a high-impedance state. In other embodiments, an impedanceexhibited at a low-impedance state may be approximately in the range of5.0 to 10.0 times lower than an impedance exhibited in a high-impedancestate, for example. It should be noted, however, that claimed subjectmatter is not limited to any particular impedance ratios betweenhigh-impedance states and low-impedance states. Truth Table 1 shows thata capacitance of a variable impedance device, such as the device ofembodiment 150, may transition between a lower capacitance state, which,in an example embodiment, may comprise approximately zero, or verylittle, capacitance, and a higher capacitance state that is a function,at least in part, of a voltage applied across the CEM device.

According to an embodiment, a CEM device, which may be utilized to forma CEM switch, a CERAM memory device, or a variety of other electronicdevices comprising one or more correlated electron materials, may beplaced into a relatively low-impedance memory state, such as bytransitioning from a relatively high-impedance state, for example, viainjection of a sufficient quantity of electrons to satisfy a Motttransition criteria. In transitioning a CEM device to a relativelylow-impedance state, if enough electrons are injected and the potentialacross the terminals of the CEM device overcomes a threshold switchingpotential (e.g., V_(set)), injected electrons may begin to screen. Aspreviously mentioned, screening may operate to unlocalizedouble-occupied electrons to collapse the band-splitting potential,thereby bringing about a relatively low-impedance state.

In particular embodiments, changes in impedance states of CEM devices,such as from a low-impedance state to a substantially dissimilarhigh-impedance state, for example, may be brought about by the“back-donation” of electrons of compounds comprising Ni_(x)O_(y)(wherein the subscripts “x” and “y” comprise whole numbers). As the termis used herein, “back-donation” refers to a supplying of one or moreelectrons to a transition metal, transition metal oxide, transitionmetal compound or any combination thereof, by an adjacent molecule ofthe lattice structure, for example, comprising the transition metal,transition metal compound, transition metal oxide, or combinationthereof. Back-donation permits a transition metal, transition metalcompound, transition metal oxide, or combination thereof, to maintain anionization state that is favorable to electrical conduction under theinfluence of an applied voltage. In certain embodiments, back-donationin a correlated electron material, for example, may occur responsive touse of a carbon containing dopant, such as carbonyl (CO), for example,which permits a correlated electron material to exhibit a property inwhich electrons are controllably, and reversibly, “donated” to aconduction band of the transition metal or transition metal oxide, suchas nickel, for example, during operation of a device or circuitcomprising a correlated electron material. Back donation may bereversed, for example, in nickel oxide material (e.g., NiO:CO), therebypermitting the nickel oxide material to switch to exhibiting asubstantially dissimilar impedance property, such as a high-impedanceproperty, during device operation. Thus, in this context, aback-donating material refers to a material that exhibits an impedanceswitching property, such as switching from a first impedance state to asubstantially dissimilar second impedance state (e.g., from a relativelylow impedance state to a relatively high impedance state, or vice versa)based, at least in part, on influence of an applied voltage to controldonation of electrons, and reversal of the electron donation, to andfrom a conduction band of the material.

In some embodiments, by way of back-donation, a CEM switch comprising atransition metal, transition metal compound, or a transition metaloxide, may exhibit low-impedance properties if the transition metal,such as nickel, for example, is placed into an oxidation state of 2+(e.g., Ni²⁺ in a material, such as NiO:CO). Conversely, electronback-donation may be reversed if the transition metal, such as nickel,for example, is placed into an oxidation state of either 1+ or 3+.Accordingly, during operation of a correlated electron material device,back-donation may result in “disproportionation,” which may comprisesubstantially simultaneous oxidation and reduction reaction,substantially in accordance with expression 4, below:2Ni²⁺→Ni¹⁺+Ni³⁺  (4)Such disproportionation, in this instance refers to formation of nickelions as Ni¹⁺+Ni³⁺ as shown in expression (4), which may bring about, forexample, a relatively high-impedance state during operation of the CEMdevice. In an embodiment, a carbon-containing ligand, such as a carbonylmolecule (CO), may permit sharing of electrons during operation of theCEM device so as to permit the disproportionation reaction of expression4, and its reversal, substantially in accordance with expression 5,below:Ni¹⁺+Ni³⁺→2Ni²⁺  (5)As previously mentioned, reversal of the disproportionation reaction, asshown in expression (5), permits nickel-based CEM to return to arelatively low-impedance state

In embodiments, depending on a molecular concentration of NiO:CO, forexample, which may vary from values approximately in the range of anatomic percentage of 0.1% to 10.0%, V_(reset) and V_(set), as shown inFIG. 1A, may vary approximately in the range of 0.1 V to 10.0 V subjectto the condition that V_(set)≥>V_(reset). For example, in one possibleembodiment, V_(reset) may occur at a voltage approximately in the rangeof 0.1 V to 1.0 V, and V_(set) may occur at a voltage approximately inthe range of 1.0 V to 2.0 V, for example. It should be noted, however,that variations in V_(set) and V_(reset) may occur based, at least inpart, on a variety of factors, such as atomic concentration of aback-donating material, such as NiO:CO and other materials present inthe CEM device, as well as other process variations, and claimed subjectmatter is not limited in this respect.

In certain embodiments, atomic layer deposition may be utilized to formor to fabricate films comprising nickel oxide materials, such as NiO:CO,to permit electron back-donation during operation of the CEM device in acircuit environment, for example, to give rise to a low-impedance state.Also during operation in a circuit environment, for example, electronback-donation may be reversed so as to give rise to a substantiallydissimilar impedance state, such as a high-impedance state, for example.In particular embodiments, atomic layer deposition may utilize two ormore precursors to deposit components of, for example, NiO:CO, or othertransition metal oxide, transition metal, or combination thereof, onto aconductive substrate. In an embodiment, layers of a CEM device may bedeposited utilizing separate precursor molecules, AX and BY, accordingto expression (6a), below:AX_((gas))+BY_((gas))=AB_((solid))+XY_((gas))  (6a)Wherein “A” of expression (6a) corresponds to a transition metal,transition metal compound, transition metal oxide, or any combinationthereof. In embodiments, a transition metal oxide may comprise nickel,but may comprise other transition metals, transition metal compound,and/or transition metal oxides, such as aluminum, cadmium, chromium,cobalt, copper, gold, iron, manganese, mercury, molybdenum, nickelpalladium, rhenium, ruthenium, silver, tin, titanium, vanadium. Inparticular embodiments, compounds that comprise more than one transitionmetal oxide may also be utilized, such as yttrium titanate (YTiO₃).

In embodiments, “X” of expression (6a) may comprise a ligand, such asorganic ligand, comprising amidinate (AMD), dicyclopentadienyl (Cp)₂,diethylcyclopentadienyl (EtCp)₂,Bis(2,2,6,6-tetramethylheptane-3,5-dionato) ((thd)₂), acetylacetonate(acac), bis(methylcyclopentadienyl) ((CH₃C₅H₄)₂), dimethylglyoximate(dmg)₂, 2-amino-pent-2-en-4-onato (apo)₂, (dmamb)₂ wheredmamb=1-dimethylamino-2-methyl-2-butanolate, (dmamp)2 wheredmamp=1-dimethylamino-2-methyl-2-propanolate,Bis(pentamethylcyclopentadienyl) (C₅(CH₃)₅)₂ and carbonyl (CO)₄.Accordingly, in some embodiments, nickel-based precursor AX maycomprise, for example, nickel amidinate (Ni(AMD)), nickeldicyclopentadienyl (Ni(Cp)₂), nickel diethylcyclopentadienyl(Ni(EtCp)₂), Bis(2,2,6,6-tetramethylheptane-3,5-dionato)Ni(II)(Ni(thd)₂), nickel acetylacetonate (Ni(acac)₂),bis(methylcyclopentadienyl)nickel (Ni(CH₃C₅H₄)₂, Nickeldimethylglyoximate (Ni(dmg)₂), Nickel 2-amino-pent-2-en-4-onato(Ni(apo)₂), Ni(dmamb)₂ wheredmamb=1-dimethylamino-2-methyl-2-butanolate, Ni(dmamp)₂ wheredmamp=1-dimethylamino-2-methyl-2-propanolate,Bis(pentamethylcyclopentadienyl) nickel (Ni(C₅(CH₃)₅)₂, and nickelcarbonyl (Ni(CO)₄), just to name a few examples; organometalliccompounds of other transition or lanthanide metals will be apparent fromthis list. In expression (6a), precursor “BY” may comprise an oxidizer,such as oxygen (O₂), ozone (O₃), nitric oxide (NO), nitrous oxide (N₂O),hydrogen peroxide (H₂O₂), just to name a few examples. In otherembodiments, plasma may be used with an oxidizer to form oxygenradicals.

However, in particular embodiments, a dopant precursor in addition toprecursors AX and BY may be utilized to form layers of the CEM device.An additional dopant precursor, which may co-flow with precursor AX, maypermit formation of back-donating compounds, substantially in accordancewith expression (6b), below. In embodiments, one or more dopantprecursors such as methane (CH₄), ethane (C₂H₆), propane (C₃H₈), butane(C₄H₁₀), acetylene (C₂H₂), carbon monoxide (CO), and/or carbon dioxide(CO₂) as well as mixtures thereof, may be utilized, as may otherprecursors comprising. Thus, expression (6a) may be modified to includean additional dopant ligand substantially in accordance with expression(6b), below:AX_((gas))+(CO or other ligand comprisingcarbon)+BY_((gas))=AB:CO_((solid))+XY_((gas))  (6b)

It should be noted that concentrations, such as atomic concentration, ofprecursors, such as AX, BY, and CO (or other ligand comprising carbon)of expressions (6a) and (6b) may be adjusted so as to bring about afinal atomic concentration of carbon in a fabricated CEM device, such asin the form of carbonyl (CO), of between approximately 0.1% and 10.0%.However, claimed subject matter is not necessarily limited to theabove-identified precursors and/or atomic concentrations. Rather,claimed subject matter is intended to embrace all such precursorsutilized in atomic layer deposition, chemical vapor deposition, plasmachemical vapor deposition, sputter deposition, physical vapordeposition, hot wire chemical vapor deposition, laser enhanced chemicalvapor deposition, laser enhanced atomic layer deposition, rapid thermalchemical vapor deposition or the like, utilized in fabrication of CEMdevices. In expressions (6a) and (6b), “BY” may comprise an oxidizer,such as oxygen (O₂), ozone (O₃), nitric oxide (NO), hydrogen peroxide(H₂O₂), just to name a few examples. In other embodiments, plasma may beused with an oxidizer (BY) to form oxygen radicals. Likewise, plasma maybe used with the carbon doping species to form an activated carbonspecies.

In particular embodiments, such as embodiments utilizing atomic layerdeposition, a substrate may be exposed to precursors in a heatedchamber, which may attain, for example, a temperature approximately inthe range of 20.0° C. to 1000.0° C., for example, or betweentemperatures approximately in the range of 20.0° C. and 500.0° C. incertain embodiments. In one particular embodiment, in which atomic layerdeposition of NiO:CO is performed, temperature ranges approximately inthe range of 20.0° C. and 400.0° C. may be utilized. After exposure toprecursor sources, such sources may be purged from the heated chamber,wherein purging may occur over durations approximately in the range of0.5 seconds to 180.0 seconds. It should be noted, however, that theseare merely examples of potentially suitable temperatures and exposuretimes, and claimed subject matter is not limited in this respect.

In certain embodiments, a single two-precursor cycle (e.g., AX and BY,as described with reference to expression 6(a)) or a singlethree-precursor cycle (e.g., AX, NH₃ or other ligand comprisingnitrogen, and BY, as described with reference to expression 6(b))utilizing atomic layer deposition may bring about a CEM device layercomprising a thickness approximately in the range of 0.6 Å to 1.5 ÅAccordingly, in an embodiment, to form a CEM device film comprising athickness of approximately 500 Å utilizing an atomic layer depositionprocess, 800-900 two-precursor (expression 6(a)) or three-precursor(expression 6(b)) cycles may be utilized. It should be noted that atomiclayer deposition may be utilized to form CEM device films having otherthicknesses, such as thicknesses approximately in the range of 200 Å and1000 Å, for example, and claimed subject matter is not limited in thisrespect.

In particular embodiments, responsive to one or more two-precursorcycles (e.g., AX and BY), or three-precursor cycles (AX, CO or otherligand comprising carbon, and BY), of atomic layer deposition, a CEMdevice film may undergo in situ annealing, which may permit improvementof film properties or may be used to incorporate the carbon-containingdopant, such as in the form of carbonyl, in the CEM device film. Incertain embodiments, a chamber may be heated to a temperatureapproximately in the range of 20° C. to 1000° C. However, in otherembodiments, in situ annealing may be performed utilizing temperaturesapproximately in the range of 150° C. to 800° C. In situ annealing timesmay vary from duration approximately in the range of 1 second to 5hours. In particular embodiments, annealing times may vary within morenarrow ranges, such as, for example, from approximately 0.5 minutes toapproximately 180 minutes, for example, and claimed subject matter isnot limited in these respects.

FIG. 1C shows one implementation of a storage element comprising acorrelated electron switch. The CES element 130, which may function as acorrelated electron random access memory (CeRAM), comprises anarrangement in which a switching region 132 is provided between tworelatively conductive regions 133. The conductive regions, 132, maycomprise or be provided with respective terminal electrodes, regions131, for the storage element.

The conductive regions, 133, may comprise a correlated electron materialthat is doped to a different level, such as a relatively higher levelcompared to region 132, such that they are relatively more conducting atthe operating voltages applied to the element than region 132. Suitablematerials for the conductive regions include transition metals,transition metal oxides, and transition metal compounds doped withligands such as carbonyl (CO), for example NiO:CO.

The switching region 132 comprises a correlated electron material whichis capable of switching from a conductor state to an insulator state(and vice-a-versa) at an operating voltage applied to the element.Suitable correlated electron materials for the switching region includedoped and undoped transition metals, transition metal compounds, andtransition metals oxides, for example NiO:CO which are capable of actingas a Mott insulator, a charge exchange insulator or an Anderson disorderinsulator under the operating conditions of the element.

In FIG. 1C, the storage element may comprise one that has been tuned byselection of relative amounts of dopant across the thin film layers toan optimum performance, for example, as a memory storage element.

For example, in the case that the dopant is a p-type dopant (forexample, carbonyl) providing that the thin film is hole conducting, thefirst, second and third amounts of dopant may provide a doping profilefor the conductive regions and the switching region which may bedescribed as p+/p/p+ or p/p+/p where p indicates that the dopingprovides for hole conducting in a conductive or switching region and +indicates the relative amount of doping in those regions.

FIG. 2A shows a simplified flowchart for a method for fabricatingcorrelated electron device materials according to an embodiment 201.Example implementations, such as described in FIGS. 2A, 2B, and 2C, forexample, may include blocks in addition to those shown and described,fewer blocks, or blocks occurring in an order different than may beidentified, or any combination thereof. In an embodiment, a method mayinclude blocks 210, 220, 230, 240 and 250, for example. The method ofFIG. 2A may accord with the general description of atomic layerdeposition previously described herein. The method of FIG. 2A may beginat block 210, which may comprise exposing the substrate, in a heatedchamber, for example, to a first precursor in a gaseous state (e.g.,“AX”), wherein the first precursor comprises a transition metal oxide, atransition metal, a transition metal compound or any combinationthereof, and a first ligand (the ligand need not comprise a carbondopant source). Examples of carbon-containing ligands for nickelprecursors include nickel cyclopentadienyl Ni(Cp)₂, nickelbis(methylcyclopentadienyl), and Nickel dimethylglyoximate; to name afew. The method may continue at block 220, which may comprise removingthe excess precursor AX and byproducts of AX by using an inert gas orevacuation or both. The method may continue at block 230, which maycomprise exposing the substrate to a second precursor (e.g., BY) in agaseous state, wherein the second precursor comprises a oxidizer such asoxygen (O₂), ozone (O₃), nitric oxide (NO), hydrogen peroxide (H₂O₂),nitric oxide (NO), nitrous oxide (N₂O), nitrogen dioxide (NO₂), or asource from the nitrogen oxide family (N_(x)O_(y)), or precursors withan NO₃ ligand; just to name some examples; so as to form a first layerof the film of a CEM device. In other embodiments, plasma may be usedwith an oxidizer (BY) to form oxygen radicals. The method may controlthe amounts of reactant precursors by controlling the mass flow, forexample, the oxidizing reactant precursor to the substrate during theexposure time. The mass flow can be controlled by a mass flow controller(MFC) in a precise and highly repeatable way not least because thereaction boundary layer over the substrate can be controlled by otherparameters such as pressure and the direction and speed of gas flowrelative to the substrate in a precise and highly repeatable way. Themethod may continue at block 240, which may comprise removing the excessprecursor BY and byproducts of BY through the use of an inert gas or byway of evacuation or by way of a combination of evacuation of theprocess chamber and purging of the chamber using an inert gas. Themethod may continue at block 250, which may comprise repeating theexposing of the substrate to the first and second precursors withintermediate purge and/or evacuation steps so as to form additionallayers of the film until the correlated electron material is capable ofexhibiting a ratio of first to second impedance states of at least5.0:1.0.

This general description shown in 200 describes atomic layer deposition.The amount of ligand dopant, such as CO in NiO:CO that is incorporatedwill be a key feature of the structure shown in FIG. 1C. The methoddescribes controlling the incorporation of the carbonyl in layers 133 ofembodiment 130 of FIG. 1C, relative to the switching layer 132, byadjusting the oxidizer flow rate or the oxidizer species to control thecarbon concentration.

FIG. 2B shows a simplified flowchart for a method for fabricatingcorrelated electron device materials according to an embodiment 202. Themethod of FIG. 2B may accord with the general description of chemicalvapor deposition or CVD or variations of CVD such as plasma enhancedCVD, hot wire CVD, rapid thermal CVD and others. In FIG. 2B, such as atblock 260, a substrate may be exposed to precursor AX and BYsimultaneously under conditions of pressure and temperature to promotethe formation of AB, which corresponds to a CEM. In the exemplary caseof NiO:CO, the precursor AX may be represented by Ni(Cp)2 or anothernickel containing precursor; and BY may be O2 or O3 or another oxidizer;the method here describes changing either the flow rate and or theoxidizer species as a function of time to form the structure such asshown in FIG. 1C where the relative amounts of dopant in regions 133 aredifferent, such as higher, than the amount of dopants in 132 ofembodiment 130. The method may control the relative amounts of reactantprecursors by controlling the mass flow of at least one reactantprecursor, for example, the oxidizing reactant precursor to thesubstrate. The mass flow can be controlled by a mass flow controller(MFC) in a precise and highly repeatable way not least because thereaction boundary layer over the substrate can be controlled by otherparameters such as pressure and the direction and speed of gas flowrelative to the substrate in a precise and highly repeatable way.Additional approaches may be employed to bring about formation of a CEM,such as application of direct or remote plasma, use of hot wire topartially decompose precursors, or lasers to enhance reactions asexamples of forms of CVD. The CVD film processes and/or variations mayoccur for a duration and under conditions as can be determined by oneskilled in the art of CVD until, for example, correlated electronmaterial having appropriate thickness and exhibiting appropriateproperties, such as electrical properties, such as a ratio of first tosecond impedance states of at least 5.0:1.0.

FIG. 2C shows a simplified flowchart for a method for fabricatingcorrelated electron device materials according to an embodiment 270. Themethod of FIG. 2C may accord with the general description of physicalvapor deposition or PVD or Sputter Vapor Deposition or variations ofthese and/or related methods. In FIG. 2C a substrate may be exposed in achamber, for example, to an impinging stream of precursor having a “lineof sight” under particular conditions of temperature and pressure topromote formation of a CEM comprising material AB:L_(x). The sourcetarget(s) may be, for example, AB or A and B and or L_(x) from separate“targets” wherein deposition is brought about using a stream of atoms ormolecules that are physically or thermally or by other means removed(sputtered) from a target(s) in “line of sight” of the substrate in aprocess chamber whose pressure is low enough or lower such that the meanfree path of the atoms or molecules of A or B or AB is approximately ormore than the distance from the target to the substrate. The stream ofAB (or A or B and/or L_(x)) may combine to form AB:L_(x) on thesubstrate due to conditions of the reaction chamber pressure,temperature of the substrate and other properties that are controlled byone skilled in the art of PVD and sputter deposition. In otherembodiments of PVD or sputter deposition, the ambient environment may bea source such as an oxidizer, for example O2, O3, NO, N2O, H2O2 orplasma activated O*, for example. The flow rate and/or changing theoxidizer species results in the control of the amount of carbonincorporated in the film, for example changing the oxidizer species as afunction of time to form the structure such as shown in FIG. 1C wherethe relative amounts of dopant in regions 133 are different, such ashigher, than the amount of dopants in 132 of embodiment 130. The PVDfilm deposition and its variations will continue for a time required andunder conditions as can be determined by one skilled in the art of PVDuntil correlated electron material of thickness and properties isdeposited that is capable of exhibiting a ratio of first to secondimpedance states of at least 5.0:1.0.

FIG. 3 is a diagram of a nickel dicyclopentadienyl molecule (Ni(C₅H₅)₂),which may be abbreviated as Ni(Cp)₂, and which may function as aprecursor to be utilized in fabrication of correlated electron materialsaccording to an embodiment 200 (detailed in 400) or 260. As shown inFIG. 3, a nickel atom, near the center of the nickel dicyclopentadienylmolecule, has been placed in an ionization state of +2 to form an N²⁺ion. In the example molecule of FIG. 3, an additional electron ispresent in the upper left and lower right CH⁻ sites of thecyclopentadienyl (Cp) portions of the dicyclopentadienyl ((Cp)₂)molecule. FIG. 3 additionally illustrates a shorthand notation showingnickel bonded to pentagon-shaped monomers of a dicyclopentadienylmolecule. As mentioned previously herein, a mixture of Ni(Cp)₂ and O3may be utilized as gaseous precursors in an atomic layer depositionprocess utilized to fabricate a CEM device.

FIGS. 4A-4L show sub-processes utilized in a method for fabricating afilm comprising a CEM according to an embodiment. The sub-processes ofFIGS. 4A-4L may correspond to the atomic layer deposition processutilizing precursors AX and BY of expression (6) to deposit componentsof NiO:CO onto a conductive substrate with control of the amount ofincorporated dopant, such as CO by means of adjustment of the oxidizerspecies and/or flow rate.

However, the sub-processes of FIGS. 4A-4L may be utilized, withappropriate material substitutions, to fabricate films comprising CEMthat utilize other transition metals, transition metal compounds,transition metal oxides, or combinations thereof, and claimed subjectmatter is not limited in this respect.

As shown in FIG. 4A, (embodiment 400) a substrate, such as substrate450, may be exposed to a first gaseous precursor, such as precursor AXof expression (6a), which may comprise of gaseous nickeldicyclopentadienyl (Ni(Cp)₂), gaseous nickel amidinate (Ni(AMD)), and/orgaseous nickel 2-amino-pent-2-en-4-onato, for example, for a duration ofapproximately in the range of 1.0 seconds to 120.0 seconds. In anembodiment that accords with expression (6). As previously described,atomic concentration of a first gaseous precursor, as well as exposuretime, may be adjusted so as to bring about a final atomic concentrationof nitrogen in a fabricated correlated electron material of betweenapproximately 0.1% and 10.0%, for example. However, the method tocontrol the dopant concentration may be or also be the proper pairing ofthe oxidizer and/or the oxidizer flow as shown in FIG. 4C, FIG. 4G, andFIG. 4K.

As shown in FIG. 4A, exposure of a substrate to a mixture of gaseousnickel dicyclopentadienyl (Ni(Cp)₂), for example, may result inattachment of (Ni(Cp)₂) molecules at various locations of the surface ofsubstrate 450. In embodiments, such attachment or deposition of Ni(Cp)₂may take place in a heated chamber, which may attain, for example, atemperature approximately in the range of 20.0° C. to 400.0° C. However,it should be noted that additional temperature ranges, such astemperature ranges comprising less than approximately 20.0° C. andgreater than approximately 400.0° C. are possible, and claimed subjectmatter is not limited in this respect.

As shown in FIG. 4B, (embodiment 401) after exposure of a conductivesubstrate, such as conductive substrate 450, to gaseous precursors, suchas a mixture of gaseous precursors comprising (Ni(Cp)₂), the chamber maybe purged of remaining gaseous Ni(Cp)₂, Cp ligands, and other byproductsusing purge gases such as nitrogen, argon, helium, or hydrogen asexamples. In an embodiment, for the example of a gaseous precursorcomprising a gaseous mixture of Ni(Cp)₂), the chamber may be purged forduration approximately in the range of 5.0 seconds to 180.0 seconds. Inone or more embodiments, a purge duration may depend, for example, onaffinity (aside from chemical bonding) of unreacted ligands and/or otherbyproducts, a transition metal oxide, or the like. Thus, for the exampleof FIG. 4B, if unreacted (Cp)₂ molecules were to exhibit an increasedaffinity for Ni, a larger purge duration may be utilized to removeremaining gaseous ligands, such as Cp ligands. In other embodiments,purge duration may depend, for example, on gas flow within the chamber.For example, gas flow within a chamber that is predominantly laminar maypermit removal of remaining gaseous ligands at a faster rate, while gasflow within a chamber that is predominantly turbulent may permit removalof remaining ligands at a slower rate. It should be noted that claimedsubject matter is intended to embrace purging of remaining gaseousmaterial without regard to flow characteristics within a chamber, whichmay increase or decrease a rate at which gaseous material is removed.

As shown in FIG. 4C, (embodiment 402) a second gaseous precursor, suchas precursor BY of expressions (6) may be introduced into the chamber.As previously mentioned, a second gaseous precursor may comprise anoxidizer, which may operate to displace a first ligand, such as (Cp)₂,for example, and replace the ligand with an oxygen and in some cases thedopant ligand, such as CO (embodiment 451). Accordingly, as shown inFIG. 4C, oxygen atoms may form bonds with at least some nickel atomsbonded to substrate 450 in addition to incorporate a relatively smallnumber of CO, for example. In an embodiment, precursor BY may oxidize(Ni(Cp)₂) to form a number of additional oxidizers, and/or combinationsthereof, in accordance with expression (7) below:Ni(C₅H₅)₂+O₂→NiO+potential byproducts (e.g., CO, CO₂, C₅H₅, C₅H₆, CH₃,CH₄, C₂H₅, C₂H₆, NH₃ . . . )  (7)

Wherein C₅H₅ has been substituted for Cp in expression (7). Inaccordance with FIG. 4C, a number of potential byproducts are shown,including C₂H₅, CO₂, CH₄, and C₅H₆. As is also shown in FIG. 4C,carbonyl, (CO) may remain bonded to nickel oxide complexes, such as atsites 451 in 402, for example. In embodiments, such nickel-to-carbonylbonds (e.g., NiO:CO), in an atomic concentration of between, forexample, 0.1% and 10.0% in a fabricated CEM device, may permit electronback donation which may bring about the substantially rapidconductor/insulator transition of a CEM device.

As shown in FIG. 4D, (embodiment 403) potential hydrocarbon byproducts,such as CO, CO₂, C₅H₅, C₅H₆, CH₃, CH₄, C₂H₅, C₂H₆, for example, may bepurged from the chamber. In particular embodiments, such purging of thechamber may occur for a duration approximately in the range of 5.0seconds to 180.0 seconds utilizing a pressure approximately in the rangeof 0.25 Pa to 100.0 kPa.

In particular embodiments, the sub-processes described shown in FIGS.4A-4D may be repeated until a desired thickness of correlated electronmaterial, such as a thickness approximately in the range of 5 nm to 50nm, is achieved. As previously mentioned herein, atomic layer depositionapproaches, such as shown and described with reference to FIGS. 4A-4D,for example, may give rise to a CEM device film comprising a thicknessapproximately in the range of 0.6 Å to 1.5 Å per each ALD cycle, forexample. Accordingly, to construct a CEM device film comprising athickness of 500.0 Å just as a possible example, approximately 300 to900 two-precursor cycles, utilizing AX_(gas)+BY_(gas) for example, maybe performed. The set of steps outlined in FIG. 4A-4D may be repeated asnecessary to deposit the thickness required for the outer doped regionsuch as shown in FIG. 1C, embodiments 133.

FIG. 4E-4H, similar to 4A-4D except the conditions are adjustedincluding; but not limited to the pairing of the AX, transition metal,precursor such as Ni(Cp)2 or other; and the oxidizer such as O3 (insteadof O2). The method here describes the ability of the relative reactivityof AX+BY in steps 4E-4H compared to 4A-4D allows one skilled in the artto control the dopant, such as carbonyl (CO) and provide a dopantconcentration best suited to embodiment 132 of FIG. 1C. Steps 4I-4Lrepresent the method to grow the outer layer, such as shown in FIG. 1C,embodiment 133 which may or may not be similar to steps 4A-4D.

In certain embodiments, cycles may be occasionally interspersed amongdiffering transition metals and/or transition metal oxides to obtaindesired properties. For example, in an embodiment, two atomic layerdeposition cycles, in which layers of NiO:CO may be formed, may befollowed by three atomic layer deposition cycles to form, for example,titanium oxide carbonyl complexes (TiO:CO). Other interspersing oftransition metals and/or transition metal oxides is possible, andclaimed subject matter is not limited in this respect.

In particular embodiments, after the completion of one or more atomiclayer deposition cycles, a substrate may be annealed, which may assistin controlling grain structure. For example, if atomic layer depositionproduces the number of columnar shaped grains, annealing may permitboundaries columnar-shaped grains to grow together which may, forexample, reduce resistance and/or enhance electrical current capacity ofthe relatively impedance state of the CEM device, for example. Annealingmay give rise to additional benefits, such as more evenly distributingof carbon molecules, such as carbonyl; for example, throughout the CEMdevice material, and claimed subject matter is not limited in thisrespect.

FIGS. 5A-5D are diagrams showing precursor flow and temperatureprofiles, as a function of time, which may be used in a method forfabricating correlated electron device materials according to anembodiment. A common timescale (T₀→T₉) is utilized for FIGS. 5A-5D. FIG.5A shows a gas flow profile 510 for a precursor, such as gaseous AX,according to an embodiment 501. As shown in FIG. 5B, flow of one or moreprecursor gases may be increased, so as to permit the one or moreprecursor gases to enter a chamber within which a CEM device may beundergoing fabrication. Thus, in accordance with flow profile 510, attime T₀, flow of one or more precursor gases may comprise a relativelylow value (F_(Low)), such as a flow of approximately 0.0, or othernegligible amount. At time T₁, flow of one or more precursor gases maybe increased to relatively higher value (F_(high)). At time T₂, whichmay correspond to a time approximately in the range of 1.0 seconds to120.0 seconds after time T₁, precursor gases AX gas may be evacuatedfrom the chamber, such as by purging, for example. A flow of precursorgases AX may be returned to a relatively low value, such asapproximately 0.0, until approximately time T₅, at which time a flow ofprecursor gases AX may be increased to a relatively higher value(F_(high)). After time T₅, such as at times T₆ and T₉, a flow ofprecursor gases AX may be returned to relatively low value untilincreased at a later time.

FIG. 5B shows a gas flow profile 520 for a purge gas, according to anembodiment 502. As shown in FIG. 5B, purge gas flow may be increased anddecreased so as to permit evacuation of the fabrication chamber ofprecursor gases AX and BY, for example. At time T₀, purge gas profile520 indicates a relatively high purge gas flow, which may permit removalof impurity gases within the fabrication chamber prior to time T₁. Attime T₁, purge gas flow may be reduced to approximately 0.0, which maypermit introduction of precursor AX gas into the fabrication chamber. Attime T₂, purge gas flow may be increased for duration of approximatelyin the range of 0.5 seconds to 180.0 seconds so as to permit removal ofexcess precursor gas AY and reaction byproducts from the fabricationchamber.

FIG. 5C shows a gas flow profile 530 for a precursor gas (e.g., BY), or540 for a different gas, CZ, according to an embodiment 503. As shown inFIG. 5C, precursor BY gas flow may remain at a flow of approximately0.0, until approximately time T₃, at which gas flow may be increased torelatively higher value. At time T₄, which may correspond to a timeapproximately in the range of 0.5 seconds to 180.0 seconds after timeT₃, precursor BY gas may be purged and/or evacuated from the chamber,such as by purging, for example. Precursor BY gas flow may be returnedto 0.0, until approximately time T₇, at which time precursor CZ gas flowmay be increased to a relatively higher value. At time T₈, which maycorrespond to a time approximately in the range of 0.5 seconds to 180.0seconds after time T₈, precursor CZ gas may be purged and/or evacuatedfrom the chamber, such as by purging, for example. Precursor CZ gas flowmay be returned to 0.0. Precursor BY and CZ are differentiated by theirrelative reactivity with the transition metal precursor and the abilityto incorporate the dopant ligand, L_(x).

At time T₃, purge gas flow may be decreased to relatively low value,such as approximately 0.0 m³/sec, which may permit precursor BY gas toenter the fabrication chamber. After exposure of the substrate toprecursor BY gas, purge gas flow may again be increased so as to permitremoval of precursor BY gas from the fabrication chamber, which maysignify completion of a single atomic layer of a CEM device film, forexample. After removal of precursor BY gas, precursor AX gas may bereintroduced to the fabrication chamber so as to initiate a depositioncycle of a second atomic layer of a CEM device film. In particularembodiments, the above-described process of introduction of precursor AXgas into the fabrication chamber, purging of remaining precursor AX gasfrom the fabrication chamber, introduction of precursor BY gas, andpurging of remaining precursor BY gas, may be repeated, for example,approximately in the range of 300 times to 900 times, for example.Repetition of the above-described process may bring about CEM devicefilms having a thickness dimension of, for example, betweenapproximately 20.0 nm and 100.0 nm, although claimed subject matter isnot limited in this regard. The number of cycles of AX+BY followed bythe AX+CZ followed by AX+BY allows the formation of the embodiment shownin FIG. 1C. The transition metal precursor, such as AX, for exampleNi(CP)2 may also change such that the transition is several cycles ofAX+BY followed by several cycles of DV+CZ followed by AX+BY, for exampleDV may be comprised of a different transition metal, titanium forexample, and/or different ligands on the precursor such as ethyl ormethyl ligands substituted for some or all of the cyclopentadienyls forexample.

FIG. 5D is a diagram showing a temperature profile, as a function oftime, used in a method for fabricating correlated electron devicematerials according to an embodiment. In FIG. 5D, a depositiontemperature may be raised to attain a temperature of, for example, atemperature approximately in the range of 20.0° C. to 900.0° C. However,in particular embodiments, somewhat smaller ranges may be utilized, suchas temperature ranges approximately in the range of 100.0° C. to 800.0°C. Further, for particular materials, even smaller temperature rangesmay be utilized, such as from approximately 100.0° C. to approximately600.0° C.

FIGS. 5E-5H are diagrams showing precursor flow and temperatureprofiles, as a function of time, which may be used in a method forfabricating correlated electron device materials according to anembodiment. A common timescale (T₀-T₇) is utilized for FIGS. 5E-5H. Asshown in embodiment 505 (FIG. 5E), precursor AX may be brought into afabrication chamber at time T₁, where time T₀ to time T₁ represent aperiod during which a process chamber may be purged and/or evacuatedutilizing an increased purge gas flow, such as shown by purge gasprofile 550 (e.g., embodiment 506 as shown in FIG. 5F), in preparationfor material deposition. Profile 540 indicates a relative increase inflow of precursor AX to occur at time T₁. Also at time T₁, flow of asecond reactant precursor, BY, may be increased, as shown in gas profile560 (e.g., embodiment 507, as shown in FIG. 5G) in which gas flow may beincreased at T₁. Two precursors (AX+BY or AX+CZ) may flow substantiallyat the same time for an amount of time consumed for the thickness of asingle CEM film layer until time T₂ at which BY flow will be reduced, attime T₃ which may be greater than or equal to T₂ and precursor CZ willbe increased to a relatively high flow until time T₄ at which time theflow rate of CZ will be reduced and precursor BY flow rate will beincreased until time T₆. The temperature profile shown in FIG. 5H (e.g.,embodiment 508) shows the temperature for deposition is set before ornear time T₀.

FIGS. 6A-6C are diagrams showing temperature profiles, as a function oftime, used in deposition and annealing processes for fabricating CEMdevices according to an embodiment. As shown in FIG. 6A (embodiment600), deposition may take place during an initial time span, such asfrom T₀ to T_(1m). From T₀ to T_(1m), a CEM device film may be depositedupon an appropriate substrate utilizing an atomic layer depositionprocess, for example. After deposition of a CEM device film, anannealing period may follow. In some embodiments, a number of atomiclayer deposition cycles may range from, for example, approximately 10cycles, to as many as 1000 cycles or more, and claimed subject matter isnot limited in this respect. After completion of deposition of a CEMfilm onto a suitable substrate, relatively high-temperature annealing oran annealing at a similar temperature range or lower temperature rangethan the deposition temperature may be performed. In some embodiments,and annealing process may utilize a temperature approximately in therange of 20.0° C. to 900.0° C., and occur from time T_(1n) to timeT_(1z). However, in particular embodiments, smaller ranges may beutilized, such as temperature ranges approximately in the range of100.0° C. to 800.0° C. Further, for particular materials, even smallertemperature ranges may be utilized, such as from approximately 200.0° C.to approximately 600.0° C. Annealing times may range from approximately1.0 second to approximately 5.0 hours, but may be narrowed to, forexample, durations of approximately 0.5 minutes to 180.0 minutes. Itshould be noted that claimed subject matter is not limited to anyparticular temperature ranges for annealing of CEM devices, nor isclaimed subject matter limited to any particular durations of annealing.In other embodiments the deposition method may comprise chemical vapordeposition, physical vapor deposition, sputter, plasma enhanced chemicalvapor deposition or other methods of deposition or combinations ofdeposition methods such as a combination of ALD and CVD to form a CEMfilm.

In embodiments, annealing may be performed in a gaseous environmentcomprising one or more of gaseous nitrogen (N₂), hydrogen (H₂), oxygen(O₂), water or steam (H₂O), nitric oxide (NO), nitrous oxide (N₂O),nitrogen dioxide (NO₂), ozone (O₃), argon (Ar), helium (He), ammonia(NH₃), carbon monoxide (CO), methane (CH₄), acetylene (C₂H₂), ethane(C₂H₆), propane (C₃H₈), ethylene (C₂H₄), butane (C₄H₁₀), or anycombination thereof.

As shown in FIG. 6B (embodiment 601), deposition may take place duringan initial time span, such as from T₀ to T_(2m), during which betweenapproximately 10 and approximately 500 cycles of atomic layer depositionmay be performed. At time T_(2n), an annealing period may be initiatedand may continue until time T_(2z). After time T_(2z), a second set ofatomic layer deposition cycles may occur, perhaps numbering betweenapproximately 10 and approximately 500 cycles, for example. As shown inFIG. 6B, a second set of atomic layer deposition (Deposition-2) cyclesmay occur at a slightly higher temperature than a first set of atomiclayer deposition cycles (Deposition-1).

As shown in FIG. 6C, (embodiment 602) deposition may take place duringan initial time span, such as from time T₀ to time T_(3m), during whichbetween approximately 10 and approximately 500 cycles of atomic layerdeposition may be performed. At time T_(3n), a first annealing period(Anneal-1) may be initiated and may continue until time T_(3z). At timeT_(3j) a second set of atomic layer deposition cycles (Deposition-2) maybe performed until time T_(3k), at which a chamber temperature may beincreased so that a second annealing period (Anneal-2) may occur, suchas beginning at time T_(3l), for example.

As used herein, the term “substrate” may include, bare silicon,silicon-on-insulator (SOI) or silicon-on-sapphire (SOS) technology,doped and/or undoped semiconductors, epitaxial layers of siliconsupported by a base semiconductor foundation, complementary metal oxidesemiconductors (CMOS), such as a CMOS front end with a metal backend,and/or other semiconductor structures and/or technologies, including CEMdevices, for example. In embodiments, a substrate may comprise a groupIII-nitride such as aluminum nitride or gallium nitride; or group III-Vmaterials such as gallium arsenide, indium phosphide or others; or othergroup IV materials such as Ge, graphene, diamond or silicon carbide orcombinations thereof. A substrate may also comprise a metal film (suchas titanium nitride, copper, aluminum, cobalt, nickel, or othermaterials); or carbon nanotubes or carbon nanotube clusters; or otherconducting materials such as ruthenium oxide or other conducting oxidesupon which the CEM may be deposited. Various circuitry, such as driverand/or decode circuitry, for example, associated with operating aprogrammable memory array, for example, may be formed in and/or on asubstrate. Furthermore, when reference is made to a “substrate” in thefollowing description, previous process steps may have been utilized toform regions and/or junctions in the base semiconductor structure orfoundation.

In an embodiment, CEM devices may be implemented in any of a wide rangeof integrated circuit types. For example, numerous CEM devices may beimplemented in an integrated circuit to form a programmable memoryarray, for example, that may be reconfigured by changing impedancestates for one or more CEM devices, in an embodiment. In anotherembodiment, programmable CEM devices may be utilized as a non-volatilememory array, for example. Of course, claimed subject matter is notlimited in scope to the specific examples provided herein.

A plurality of CEM devices may be formed to bring about integratedcircuit devices, which may include, for example, a first correlatedelectron device having a first correlated electron material and a secondcorrelated electron device having a second correlated electron material,wherein the first and second correlated electron materials may comprisesubstantially dissimilar impedance characteristics that differ from oneanother. Also, in an embodiment, a first CEM device and a second CEMdevice, comprising impedance characteristics that differ from oneanother, may be formed within a particular layer of an integratedcircuit. Further, in an embodiment, forming the first and second CEMdevices within a particular layer of an integrated circuit may includeforming the CEM devices at least in part by selective epitaxialdeposition. In another embodiment, the first and second CEM deviceswithin a particular layer of the integrated circuit may be formed atleast in part by ion implantation, such as to alter impedancecharacteristics for the first and/or second CEM devices, for example.

Also, in an embodiment, two or more CEM devices may be formed within aparticular layer of an integrated circuit at least in part by atomiclayer deposition of a correlated electron material. In a furtherembodiment, one or more of a plurality of correlated electron switchdevices of a first correlated electron switch material and one or moreof a plurality of correlated electron switch devices of a secondcorrelated electron switch material may be formed, at least in part, bya combination of blanket deposition and selective epitaxial deposition.Additionally, in an embodiment, first and second access devices may bepositioned substantially adjacently to first and second CEM devices,respectively.

In a further embodiment, one or more of a plurality of CEM devices maybe individually positioned within an integrated circuit at one or moreintersections of electrically conductive lines of a first metallizationlayer and electrically conductive lines of a second metallization layer,in an embodiment. One or more access devices may be positioned at arespective one or more of the intersections of the electricallyconductive lines of the first metallization layer and the electricallyconductive lines of the second metallization layer, wherein the accessdevices may be paired with respective CEM devices, in an embodiment.

In the preceding description, various aspects of claimed subject matterhave been described. For purposes of explanation, specifics, such asamounts, systems, and/or configurations, as examples, were set forth. Inother instances, well-known features were omitted and/or simplified soas not to obscure claimed subject matter. While certain features havebeen illustrated and/or described herein, many modifications,substitutions, changes, and/or equivalents will occur to those skilledin the art. It is, therefore, to be understood that the appended claimsare intended to cover all modifications and/or changes as fall withinclaimed subject matter.

What is claimed is:
 1. A film deposited on a substrate, comprising: acorrelated electron material comprising a carbon-based material as anelectron back-donating material, in an atomic concentration of carbonbetween 0.1% and 10.0%, the film having an approximate thickness ofbetween 1.5 nm and 150.0 nm and exhibiting a ratio of a first resistancestate to a second resistance state of at least 5.0:1.0 when a voltage ofbetween of 0.1 V and 10.0 V is applied across a thickness dimension ofthe film.
 2. The film according to claim 1, wherein the correlatedelectron material comprises a thickness of between 10.0 nm and 50.0 nmand exhibits a ratio of a first resistance state to a second resistancestate of at least 5.0:1.0 when a voltage of between 0.6 V and 1.5 V isapplied across a thickness dimension of the film.
 3. The film accordingto claim 1, wherein the correlated electron material comprises between10 and 1000 atom layers.
 4. The film according to claim 1, wherein thecarbon-based material provides for p-type doping of the correlatedelectron material film.
 5. The film according to claim 1, wherein thecorrelated electron material film comprises a switching region ofcorrelated electron material disposed between a first relativelyconductive region of correlated electron material and a secondrelatively conductive region of correlated electron material.
 6. Thefilm according to claim 5, wherein the switching region has an atomicconcentration of carbon less than that of each of the first and thesecond relatively conductive regions.
 7. The film according to claim 5,wherein the switching region exhibits a first impedance state and theconductive regions exhibit a second impedance state, and wherein thefirst impedance state and the second impedance are substantiallydissimilar from one another.
 8. The film according to claim 1, whereinthe correlated electron material film comprises a transition metal or atransition metal oxide.
 9. The film according to claim 1, wherein thecorrelated electron material film comprises at least one first atomlayer of correlated electron material interspersed between at least twosecond atom layers of correlated electron material, and wherein the atleast one first atom layer of correlated electron material comprises atransition metal or a transition metal oxide which is different fromthat of the correlated electron material of the at least two second atomlayers.
 10. The film according to claim 1, wherein the correlatedelectron material comprises nickel oxide and the carbon-based materialcomprises carbonyl ligand.
 11. A switching device, comprising: acorrelated electron material film comprising a carbon-based material asan electron back-donating material in an atomic concentration of carbonof between 0.1% and 10.0%, the correlated electron material film beingdisposed between two or more conductive electrodes, the correlatedelectron material having a thickness of between 1.0 nm and 150.0 nm andexhibiting a ratio of a first resistance state relative to a secondresistance state of at least 5.0:1.0 when a voltage of between 0.1 V and10.0 V is applied across at least two of the two or more conductiveelectrodes.
 12. The switching device according to claim 11, wherein thecorrelated electron material film comprises a thickness of between 10.0nm and 50.0 nm and exhibits a ratio of a first resistance state relativeto a second resistance state of at least 5.0:1.0 when a voltage ofbetween 0.6 V and 1.5 V is applied across at least two of the two ormore conductive electrodes.
 13. The switching device according to claim11, wherein one or more of the conductive electrodes comprise titaniumnitride, platinum, titanium, copper, aluminum, cobalt, nickel, tungsten,tungsten nitride, cobalt silicide, ruthenium oxide, chromium, gold,palladium, indium tin oxide, tantalum, silver or iridium, or anycombination thereof.
 14. The switching device according to claim 11,wherein the carbon-based material provides for p-type doping of thecorrelated electron material film.
 15. The switching device according toclaim 11, wherein the correlated electron material film comprises aswitching region of correlated electron material disposed between afirst relatively conductive region of correlated electron material and asecond relatively conductive region of correlated electron material. 16.The switching device according to claim 15, wherein the switching regionhas an atomic concentration of carbon less than that of each of thefirst and the second relatively conductive regions.
 17. The switchingdevice according to claim 15, wherein the switching region exhibits afirst impedance state and the conductive regions exhibit a secondimpedance state, and wherein the first impedance state and the secondimpedance are substantially dissimilar from one another.
 18. Theswitching device according to claim 11, wherein the correlated electronmaterial film comprises a transition metal or a transition metal oxide.19. The switching device according to claim 11, wherein the correlatedelectron material film comprises at least one first atom layer ofcorrelated electron material interspersed between at least two secondatom layers of correlated electron material, and wherein the at leastone first atom layer of correlated electron material comprises atransition metal or a transition metal oxide which is different fromthat of the correlated electron material of the at least two second atomlayers.
 20. The switching device according to claim 11, wherein thecorrelated electron material film comprises nickel oxide and thecarbon-based material comprises carbonyl ligand.